We will study a) intrahippocampal mechanisms of the theta rhythm of rats and b) the relation of the firing of hippocampal neurons to the behavior of rats in three different situations. We will determine the relation of firing of neurons in hippocampus, medial septal nucleus, and entorhinal cortex to phase of theta rhythm, the change in monosynaptic population spikes as a function of phase of theta rhythm, and the changes in theta rhythm after lesions of fornix-fumbria and entorhinal cortex. From these and other data we hope to construct a quantitative model of intrahippocampal mechanisms and cellular interaction during the theta rhythm. A single complex spike cell will be recorded from while a maternal rat runs an eight-arm Olton maze, performs a DRL-16, and during pup retrieval. We will look for aspects of the firing of each neuron which are common to all three situations. Our overall goal is to understand the relation of the firing of hippocampal neurons to behavior and how these neurons interact with each other.